Electronic article surveillance (EAS) systems are widely used to detect the presence of small electronic labels placed on or in an article or carried by a person of interest, and can, for example, be used in retail or library environments to deter theft or other unauthorized removal of articles. In particular, EAS labels are attached to articles designated to either be purchased or borrowed, and when active, will trigger an alarm if an article is carried without authorization through interrogation zones typically located at the store or library exits.
There are many applications for when users also desire to know more information than just whether a tagged object is present. For example, very often users also want to know which tagged article is present. In this connection, information-carrying tags are widely used both for the identification of products and security purposes. These information tags are able to carry a sufficient number of bits regarding the characteristics of articles to provide useful information, such as the product's name, date of manufacture, price, and whether the product, article or person has properly passed through a check-out counter or kiosk, etc. As used herein, the terms “information carriers”, “marks”, “markers”, “labels” and “tags” are used interchangeably and refer to the devices used to carry multi-bit data therein.
The most popular example of the information-carrying multi-bit tags is a printed optical barcode. Another known technique of electronic item identification is based on the use of a Radio Frequency (RF) tag. RF tags have been developed and are disclosed, for example, in the following publications: U.S. Pat. No. 5,574,470 to de Vall; U.S. Pat. No. 5,625,341 to Giles et al.; U.S. Pat. No. 5,682,143 to Brady et al; U.S. Pat. No. 5,995,006 to Walsh; U.S. Pat. No. 6,100,804 to Brady et al.; U.S. Pat. No. 6,104,311 to Lastinger; U.S. Pat. No. 6,304,169 to Blama et al; U.S. Pat. No. 6,346,884 to Uozumi et al; U.S. Pat. No. 6,424,263 to Lee et al; U.S. Pat. No. 6,441,740 to Brady et al. Such information carrying tags are responsive to a coded RF signal received from a base station.
Generally, RF tags can be active (i.e., utilizing an internal energy source incorporated with the tag) or passive, that function using the energy of an external interrogation signal and are dependant on energy supplied from a tag reader or an external device. The RF tag typically includes an antenna attached to a resonance circuit, which is energized (e.g., by the received interrogation signal) and which, when energized, excites the antenna to transmit an RF response signal at a resonance frequency of the circuit. The antennas used in an RF ID tag are generally constituted by loops of wire or metal etched or plated on the tag surface.
The particulars and advantageous features of active and passive RF tags are described for example in the article, “Active and Passive RFID”, Savi Technology, White paper, January 2002.
RF ID tags may have various code or memory configurations. The most simple is the single code tag typically utilized in EAS systems. These tags emit a single response when activated by a reader. The response is a simple “yes” or “no” indicating whether or not the tag is present or activated. Other tags respond with a code including a preset serial number. It is also known to provide a plurality of resonant circuits on an RF ID tag, each resonant circuit configured with the tag to output a response signal at a predetermined frequency in response to an interrogating signal. The response signals define a response code of the tag, which is determined by the number of individual circuits and the manner of their operation.
For example, U.S. Pat. No. 6,104,311 to Lastinger describes an RF identification tag comprising a substrate, an input mechanism disposed on the substrate and configured to receive a query signal, and an output mechanism disposed on the substrate. The tag includes a response circuitry disposed on the substrate in operative communication with the input/output mechanism which can be one or more antennas configured to receive and transmit signals at a predetermined frequency. The response circuitry includes one or more code circuits, each configured to output a unique response code. A connection between any given code circuit and a given antenna determines a response code and frequency at which that response code will be generated and output in the response signal. The selective connection of the code circuits and the antennas determines the response code/frequency combinations that comprise the response signal.
Another technique described in U.S. Pat. No. 6,304,169 to Blama utilizes radio frequency waves transmission between a scanning device and an RF tag in order to identify an item to which the tag is attached. The tag includes a first insulating layer having a top surface and a bottom surface, and resonant circuits formed on the first insulating layer. Each of the resonant circuits is formed on one of the top and bottom surfaces of the first insulating layer, and has a resonant frequency associated therewith. Each of the code circuits includes a code circuit (capacitance and inductance elements). The tag is associated with a binary number established by a pattern of ones and zeros depending on each circuit resonance or non-resonance, respectively.
The developments in the RF tag technology are aimed at creating the so-called chipless RFID tags (utilizing a printing technique rather than the integrated technology), such as disclosed, for example, in the following Internet Sites:                http://www.checkpointsystems.com/downloads/pdf/es105.pdf        http://www.checkpointsystems.com/downloads/pdf/es102.pdf        